1. Field of the Invention
The present invention relates to an apparatus for the supply of a breathing gas to a patient.
2. Description of the Prior Art
An apparatus, such as a ventilator or respirator, for supplying a breathing gas to a patient, in which a supply means is operated to continuously generate a flow of gas, is disclosed in European Application 0 813 883. The apparatus disclosed therein has a fan or compressor which may be continuously operated to provide a flow of a breathable gas to a flow divider. The flow divider operates to divert the gas flow either toward a patient during an inspiration phase of the patient""s breathing cycle or to a recirculating system during an expiration phase, to be re-directed toward the patient in the subsequent inspiration phase. Since the supply means is operated continuously, changes in supply to the patient can be made rapidly by varying only the relatively responsive flow divider. The gas supplied by the supply means, however, is not usefully employed during the expiration phase and the energy used in powering the supply means may be considered as being wasted.
It is an object of the present invention to provide an apparatus in which gas supplied by a supply arrangement can be usefully employed during an expiration phase of a patient.
By providing the expiration tube with a venturi outlet and arranging for gas from the supply to pass across this outlet, preferably at an angle of 90xc2x0 or less to the direction of expiration gas flow from the outlet, during an expiration phase then expiration effort expended by the patient can be reduced.
The supply, such as a compressor or fan assembly, can be operated to continuously generate a flow of breathable gas throughout the patient""s breathing cycle. This has the advantage that no additional gas source need be included within the supply for supplying gas during the expiration phase.
A vane deflector, rotatable in the flow path of the gas from the supply, for selectively coupling the flow to the inspiration or expiration lines may be used. This provides a relatively simple and inexpensive flow controller.
Additionally, the supply can be operated to provide a flow greater than that required during an inspiration phase. This means that the vane need not deflect all gas flow into the inspiration line. This avoids problems, such as incorrect switching between the inspiration and the expiration phases, associated with the vane sticking against a sealing surface and also allows a less expensive vane deflector to be used since manufacturing tolerances are reduced compared to a deflector in which a complete seal must be effected.
The venturi outlet may be variable in size to allow control of the venturi effect and hence the expiration effort of a patient. This may be simply achieved by arranging for the vane of the vane deflector to be cooperable with the end of the expiration line to form a venturi outlet that varies as the deflector moves.